The present invention relates generally to interventional catheters and prostheses, and more specifically to catheters and prostheses for treatment of vascular diseases, including coronary artery disease and peripheral vascular disease, as well as diseases of other body lumens such as the biliary tract, fallopian tubes, urinary and digestive tracts, and other structures.
Balloon angioplasty and stenting are widely used in the treatment of coronary artery disease and peripheral vascular disease. In coronary artery disease, one or more coronary blood vessels become narrowed or closed due to the buildup of stenotic plaques on the arterial wall. This blocks blood flow to the heart muscle, potentially causing myocardial infarction. Such narrowing can also occur in peripheral blood vessels such as the carotids, femorals, iliacs and other arteries, blocking the blood supply to other vital tissues and organs.
Balloon angioplasty involves the use of a long flexible catheter having a balloon at its distal tip. The catheter is inserted into a peripheral artery such as the femoral and advanced transluminally into the diseased artery. The balloon is inflated within the narrowed portion of the vessel, thereby expanding the vascular lumen and restoring normal blood flow.
In some cases, however, balloon angioplasty alone is inadequate to treat vascular disease due to restenosis, the renarrowing of the artery following angioplasty. Stents have been developed to provide an intravascular frame or scaffold to maintain patency of the vascular lumen after it has been expanded. Stents are small tubular prostheses designed to be advanced to the treatment site in a collapsed configuration using an elongated delivery catheter. The stents are then expanded at the treatment site into engagement with the vessel wall to maintain vascular patency.
Stents may be either self-expanding or balloon expandable. Self-expanding stents are made of a shape memory material such as Nitinol and can be delivered in a compressed state within the tip of the delivery catheter and allowed to resiliently expand upon release from the delivery catheter. Balloon expandable stents are made of a malleable metal and are mounted to a balloon on the delivery catheter. When positioned at the treatment site, the balloon is inflated to expand the stent into engagement with the vessel.
Stents, however, have also suffered from the problem of restenosis. Restenosis rates with conventional coronary stents have ranged from 30-40%. The causes of such restenosis are not fully understood. However, it is believed that restenosis may be caused in some cases by the excessive stiffness of current stents and their inability to conform to vascular curves, shapes, dimensional changes, and movements. This problem is particularly acute with longer lesions, which may extend over curved and tapered sections of a vessel and may be subject to non-uniform movements along their lengths.
The need has thus been demonstrated for highly flexible stents that may be used to treat long, curved, and tapered vascular regions. In co-pending U.S. patent application Ser. No. 10/637,713, filed Aug. 8, 2003, entitled “Apparatus and Methods for Delivery of Vascular Prostheses,” the full disclosure of which is incorporated herein by reference, highly flexible multi-segmented stents and associated delivery devices are disclosed that enable the treatment of long, curved or tapered vascular lesions. The disclosed delivery devices enable the selective deployment of one or more stent segments at a treatment site to allow the user to customize stent length in situ. Moreover, the device can be repositioned at multiple vascular sites to deploy a plurality of stents of various lengths.
Other custom-length stents and delivery devices are described in co-pending U.S. patent application Ser. No. 10/412,714, filed Apr. 10, 2003, entitled “Apparatus and Methods for Delivery of Multiple Distributed Stents,” (hereinafter referred to as “the '714 application”), which is also incorporated herein by reference. The '714 application describes devices for delivering multiple discrete prostheses, such as stents, in body lumens. An exemplary delivery catheter includes a sheath, a pusher for moving the prostheses relative to the sheath, and a valve member for selectively retaining the prostheses in the sheath. The valve member allows a selected number of prostheses to be deployed from the sheath while retaining other prostheses within the sheath.
The '714 application describes prosthesis delivery catheters and systems that include valve members that function either actively or passively. In passive configurations, the valve member prevents the prosthesis from exiting the passage under a first force and allows the prosthesis to exit the passage under a second force higher than the first force. In active embodiments, the valve member is selectively movable between a contracted configuration in which the valve member allows movement of prostheses out of the sheath, and an extended configuration in which the valve member inhibits movement of prostheses out of the sheath.
Variable length angioplasty devices have also been proposed. For example, U.S. Pat. No. 5,246,421 to Saab discloses angioplasty catheters having an elongated balloon and an external sheath that is axially slidable relative to the balloon. The sheath can be retracted to expose a selected length of the balloon for expansion at a treatment site. The catheter can then be repositioned and another length of balloon exposed to treat one or more additional sites.
While such custom-length stents and angioplasty catheters have shown great promise, there remains a need for improved ways of delivering multi-segment prostheses in body lumens. For example, whereas the '714 application describes several valve member embodiments, including embodiments that function both passively and actively, there remains a need for valve members that are able to effectively and consistently create separation between the distal-most prosthesis segment within the catheter shaft and the proximal-most prosthesis segment exposed distally of the shaft. Such valve members should also function while minimizing damage to the prosthesis segments or any coatings contained thereon.
For these and other reasons, stents and stent delivery catheters are needed which enable the customization of stent length in situ, and the treatment of multiple lesions of various sizes, without requiring removal of the delivery catheter from the patient. Such stents and stent delivery catheters should be capable of treating lesions of particularly long length and lesions in curved regions of a vessel, and should be highly flexible to conform to vessel shape and movement. Such stent delivery catheters should further be of minimal cross-sectional profile and should be highly flexible for endovascular positioning through tortuous vascular pathways.